1. Field of the Invention
This present invention relates to a transmission apparatus, more particularly, to a transmission apparatus that employs gears having movable gear teeth. This type of device can be used for a broad range of applications, which require motion and power to be transmitted continuously from an input element to an output element with a predetermined velocity ratio.
2. Description of the Related Art
There are known mechanical power transmission devices comprise gears having a plurality of movable gear teeth that mesh with stationary gears, such as U.S. Pat. No. 4,798,104, Chinese patent No.CN85,101,702A, Chinese patent No.CN86,200,768U, and Russian patent No.SU-1,307,129. Since sliding occurs between moving pairs among the wave generators, the movable gear teeth and their carriers, and the stationary gears, these types of devices have low transmission efficiency and high wear.
Sliding also occurs in the variable speed transmission apparatus of U.S. Pat. No. 4,856,378 because the rollers can only rotate with either the eccentric cam or the stationary gear but not both at the same time. This type of device has limited transmission ratios and loading capacity since the number of inner teeth of the stationary gear is two less than that of the rollers of the special gear, so that only a few gear teeth are engaged at any time. Furthermore, because the eccentricity of the extendable cam varies, the transmission ratio is not constant. Similarly, the loading capacity and transmission ratio of U.S. Pat. No. 3,468,175 are also limited because it requires the number of the movable gear teeth to be a harmonic of the number of the casing teeth. In addition, this design requires complicated movable gear teeth comprising five different rollers.
U.S. Pat. No. 4,713,985 provides a pure rolling-style transmission. However, the connecting elements on the carrier disk not only reduce the number of driving rollers but also increase their size. This type of transmission device has limited loading capacity because it has less engaged gear teeth. It also has limited transmission ratio because fewer driving rollers can be arranged on the carrier disk. Furthermore, the asymmetrical gear tooth profile of the casing and the structure of the connecting elements make this transmission suitable only for rotating in the pulling direction of the connecting elements.
In Chinese patent No.CN1,020,383C one of the present inventors Zhi Chen proposes an oscillatory tooth transmission which eliminates sliding from all relative moving pairs. As it is shown by FIG. 10, the oscillatory tooth gear comprises two gear tooth carriers, staggered at a half pitch of a gear tooth, and connected by a plurality of screws. Holding a row of oscillatory teeth, each gear tooth carrier comprises a force-transmitting disk 23 and an oscillatory tooth disk 22. This arrangement is difficult to produce and subject to assembly error. In addition, the oscillatory gear carrier has limited strength and stiffness.